Conventionally, for a fuel tank seal valve, there is provided a valve having a positive-pressure relief valve and negative-pressure relief valve for maintaining a pressure in a fuel tank at a proper pressure (see US 2010/0269921A1). The pressure in the fuel tank may be a positive pressure as a result of vaporization of fuel, or a negative pressure as a result of devolatilization of the vaporized fuel. Accordingly, for the purpose of protection of the fuel tank, the positive-pressure relief valve and negative-pressure relief valve are provided for keeping the pressure in the fuel tank at the proper pressure.
The positive-pressure relief valve and negative-pressure relief valve are configured to urge their valving elements in a valve-closing direction by their relief springs, respectively. Therefore, a valve-opening pressure (i.e., relief pressure) is determined by a set load of the relief spring. However, because the relief spring has a tolerance, the set load varies despite the same set length, so that a target valve-opening pressure may not be obtained. Accordingly, to set the valve-opening pressure at the target pressure, it becomes necessary to provide an adjustment mechanism for adjusting the set load of the relief spring.
However, according to the technology described in US 2010/0269921A1, a spring receiving part that receives the relief spring of the positive-pressure relief valve, and a spring receiving part that receives the relief spring of the negative-pressure relief valve are positioned on the opposite sides of a housing. Accordingly, when a mechanism for adjusting the position of the spring receiving part is employed for the mechanism for adjusting the relief spring, adjustment operations of the respective relief valves need to be performed from different directions. As a result, the adjustment operations become complicated. Specifically, after the adjustment of one relief spring, the other relief spring needs to be adjusted with the housing inverted.